Macrostomum qiaochengensis Wang & Fang

Wang, Lei, Xin, Fan, Fang, Chu-Yu, Zhang, Yu & Wang, An-Tai, 2017, Two new brackish-water species of Macrostomum (Platyhelminthes, Macrostomida) from mangrove wetland in southern China, Zootaxa 4276 (1), pp. 107-124 : 113-116

Macrostomum qiaochengensis Wang & Fang , n. sp.

( Figs. 5–7 )

Material examined. Observations were made on live and preserved specimens. Holotype (PLA–Ma0080): one mounted specimen. Paratypes (PLA–Ma0081–89): nine serially-sectioned specimens. The type specimens were collected by Chu-Yu Fang from the same location as that of M. shenzhenensis n. sp. (22°31′87″ N, 113°58′87″ E) ( Fig. 1 ). All specimens are deposited in IZCAS .

Etymology. The name of this new species is derived from the name of OCT mangrove wetland, Shenzhen City, Guangdong Province, China.

Description. The body is transparent and dorsoventrally flattened. The body length and width are 1,147 ± 52 µm (n=6) and 186 ± 7 µm (n=6) (length to width ratio is approximately 6:1) ( Figs. 5 A, 7A). Its head and tail are rounded. The anterior and posterior body margin have rigid cilia that are 8 ± 1.9 µm (n=6) long. The whole body is covered with cilia that are 6.7 ± 1.4 µm (n=6) long. The epidermis, 4 ± 0.5 µm (n=6) thick, contains a large number of rhabdites. The brain is crescent shaped, with its widest part 23 ± 1.4 µm (n=6) ( Fig. 6 A). It lies posteriorly to a pair of reniform eyes and the distance between two eyes is 28 ± 9.3 µm (n=6). The mouth is 82.6 ± 10.0 µm (n=6) long. The pharynx is ventrally surrounded by numerous saccular pharyngeal glands ( Figs. 5 A, 6C). At the caudal end of the flatworm, there are a number of well-developed adhesive glands ( Fig. 5 B).

The male reproductive system of M. qiaochengensis n. sp. conforms to the general plan within the genus Macrostomum ( Figs. 5 C–D, 6A, 6D–G, 7B–C). A pair of elongated oval-shaped testes is 115 ± 10.8 µm (n=3) long and is located at each side of the anterior 30% of the intestine. The oval-shaped false vesicula seminalis lies posterior to the female antrum on the left side. The muscular vesicula seminalis is also oval shaped and connects to the posterior tear-shaped vesicula granulorum. The vesicula granulorum is partially enclosed by the proximal end of the hook-shaped penis stylet. The proximal end of the penis stylet is 21 ± 1.2 µm (n=8) broad. The curved-line (marked as ‘a’) and straight-line (marked as ‘b’) between the proximal and distal ends of the stylet are 51 ± 3.5 µm (n=8) and 45 ± 3.3 µm (n=8), respectively ( Fig. 7 C). The anterior 63% of the penis stylet is funnel shaped, while the rest is willow leaf shaped and forms a right angle with the anterior part ( Figs. 5 E–G, 7D). The stylet opens at the convex side, starts from the position of the curve (anterior 63%), and ends in the distal tip ( Figs. 5 H–I). The features of the female reproductive system are similar to those of the above mentioned M. shenzhenensis n. sp. ( Figs. 5 A–B, 6B, 6D, 6F–G). Except its female atrium locates at the posterior end of the intestine in M. qiaochengensis n. sp..

The mature sperm are 88 ± 3.6 µm (n=6) long ( Figs. 5 J–K, 7E). The lengths of feeler, body and shaft of the sperm are 24 ± 1.7 µm, 17 ± 1.6 µm and 46 ± 3.6 µm (n=6). Diameters of the feeler, body and shaft are 0.6 ± 0.2 µm (n=6), 2.0 ± 0.7 µm (n=6) and 1.3 ± 0.2 µm (n=6), respectively. A pair of bristles, 14 ± 1.6 µm (n=6) long, is on the sperm body. While 3–7 brushes, 3 ± 0.7 µm (n=8) long, can be observed at the posterior end of the shaft.

Remarks. A comparison of the penis stylets between Macrostomum qiaochengensis n. sp. and six other previously-described resembling species of Macrostomum is shown in TABLE 2. They are common in the following characteristics: 1) hook-like overall morphology; 2) rigid and pointed distal end. However, stylets of these species vary in the position of distal opening. For example, in M romanicum , the position of the opening is 64% of the stylet length, while in most of the other species, the distal opening is located at a position larger than 70% of the stylet length. Moreover, its stylet length is much longer than that of M. qiaochengensis n. sp.. As for the position of the curve in the stylet, M. hystrix (63%) is similar to M. qiaochengensis n. sp. (63%). However, the bending angle of M. hystrix (77°) is much smaller than that of M. qiaochengensis n. sp. (90°). In M. qiaochengensis n. sp., the stylet bends sharply and forms a right angle at 63% of its length ( Figs. 5 E–F, 5H), while the opening starts from the position of the curve to the distal tip of the stylet and is willow leaf shaped. Therefore, obvious differences can be noticed between M. qiaochengensis n. sp. and the six resembling species of Macrostomum .

* Measurement based on images and scales from the references. The procedures of measuring the angle refer to Ferguson (1940).

NA: Not available, information cannot be obtained from literature.

Molecular phylogenetic analysis. Phylogenetic analyses using neighbor joining (NJ) and maximum likelihood (ML) methods ( Figs. 8–13 ) showed that three specimens of M. shenzhenensis n. sp., as well as those of M. qiaochengensis n. sp. cluster together. Furthermore, all of these results show that these two new species form a well-supported clade with M. hystrix and M. lignano , which is in good agreement with the morphological comparison of these species. In summary, both morphological and phylogenetic evidence supports the establishments of M. shenzhenensis n. sp. and M. qiaochengensis n. sp. as new species.

Figures

FIGURE 1. The locations of the two new species of Macrostomum in Guangdong Province, China.

FIGURE 5. Macrostomum qiaochengensis Wang & Fang, n. sp.: (A) mature living animal, ventral view; (B) posterior part of the body, ventral view; (C – D) copulation apparatus (slightly squeezed), ventral view; (E – G) penis stylet; (H & I) penis stylet opening; (J & K) mature sperm.

FIGURE 6. Macrostomum qiaochengensis Wang & Fang, n. sp.: (A – C) horizontal whole body section; (D – G) longitudinal whole body section.

FIGURE 7. Macrostomum qiaochengensis Wang & Fang, n. sp.: (A) whole body, ventral view; (B) profile of the tail; (C) copulatory apparatus; (D) penis stylet; (E) mature sperm.

FIGURE 8. The phylogenetic tree of 18 S rDNA generated with Maximum Likelihood method. (bootstrap = 1000, Tamura-nei type)

FIGURE 9. The phylogenetic tree of 18 S rDNA gene generated with Neighbor-Joining method. (bootstrap = 1000, Kimura 2 - parameter type)

FIGURE 10. The phylogenetic tree of 28 S rDNA generated with Maximum Likelihood method. (bootstrap = 1000, Tamura-nei type)

FIGURE 11. The phylogenetic tree of 28 S rDNA gene generated with Neighbor-Joining method. (bootstrap = 1000, Kimura 2 - parameter type)

FIGURE 13. The phylogenetic tree of the concatenated sequences of 18 S and 28 S rDNA genes with Neighbor-Joining method. (bootstrap = 1000, Kimura 2 - parameter type)